Communications and data transmission systems that transmit information signals in the form of optical pulses over optical fiber are now commonplace, and optical fibers have become the physical transport medium of choice in long distance telephone and data communication networks due to their signal transmission capabilities, which greatly exceed those of mechanical conductors. Despite their advantages, however, difficulties in their manufacture must be overcome in order for high-yield, high-quality and error-free optical fiber to be produced in mass. One such manufacturing problem is mechanical twist.
Mechanical twist of an optical fiber induces PMD, which is undesirable as it negatively impacts the performance of an optical fiber. More specifically, mechanical twist is caused by an external torque placed on the fiber due to misalignment of the draw tower, which causes stress-induced birefringence that increases PMD in a spun optical fiber. Mechanical twist is illustrated in FIG. 1A. As shown in FIG. 1A, mechanical twist, represented by the directional arrow, is caused by an external twisting of the coating 2 of an optical fiber. This twisting causes a non-uniform stress on the glass fiber 4, resulting in increased PMD. Mechanical twist is distinguishable from fiber spin, which is a desirable feature produced by the purposeful rotation of the optical fiber core during manufacture. Fiber spin, illustrated by the directional arrow in FIG. 1B, is induced during formation of the optical fiber 4 by rotating the drawn glass which forms the optical fiber core.
Because mechanical twist is an unwelcome occurrence in the manufacturing process of optical fiber, once mechanical twist is detected optical fiber manufacturing equipment can be adjusted to minimize the degree of mechanical twist imparted to an optical fiber. However, this correction adjustment does not correct optical fiber that has already been created by an imperfect manufacturing process.
Therefore, what is needed is a system, method and apparatus to correct mechanical twist in optical fiber post draw, i.e., after the optical fiber has been manufactured.